The invention pertains to new catalyst systems for polycondensation reactions.
The synthesis of polyesters, for example polyethylene terephthalate, requires the use of catalysts in the polycondensation step. The literature contains an abundance of patents describing the use of various catalytically active substances. Today especially antimony and titanium compounds are used on a large industrial scale in the manufacturing of polyethylene terephthalate. This is also reflected in the large number of patents that describe the use of such compounds. Polyester-soluble antimony compounds are described in U.S. Pat. Nos. 3,965,071; 3,998,793; 4,039,515; 4,116,942; 4,133,800; 4,454,312; 5,750,635; and 5,780,575 as polycondensation catalysts. Modified antimony derivatives (stabilization by substances with double bonds to prevent reduction to metallic antimony) are, for example, subjects of U.S. Pat. Nos. 4,067,856; 4,067,857; and 4,130,552. Antimony salts of trimellitic acid esters are likewise used as catalysts in the manufacturing of polyethylene terephthalate (U.S. Pat. No. 5,478,796). Titanium derivatives, especially tetraalkyl titanates, are protected in the U.S. Pat. Nos. 4,039,515; 4,131,601; 4,482,700; 5,066,766; 5,302,690; WO 97/45470; and U.S. Pat. No. 5,744,571. A combination of sulfonic acid, titanate and antimony (or germanium) compound is the subject of U.S. Pat. No. 5,905,136. Germanium compounds are also described as catalysts for the polycondensation reaction (U.S. Pat. No. 5,378,796; 5,830,981; 5,837,786; and 5,837,800). Catalytically active compounds in a polycondensation reaction are likewise borates and acetates of zinc, calcium, cobalt, lead, cadmium, lithium, or sodium (U.S. Pat. No. 4,115,371).
Defined silicon compounds (2-cyanoethyltriethoxysilane and 3-aminopropyltriethoxysilane) are protected in a US Patent (U.S. Pat. No. 4,077,944) as polycondensation catalysts.
The combination of several metal compounds is described in the following patents: U.S. Pat. No. 4,080,317 (Sb/Pb/Zn, Sb/Pb/Ca, Sb/Zn, Sb/Pb/Mg, Sb/Pb/Ca/Mn, Sb/Pb/Ca/Zn, Sb/Pb/Li, Sb/Mn, Ti/Ca, Ge/Ga, Ge/Zn, and Ge/K); U.S. Pat. No. 4,104,263 (Sb(Zr)/Zn(Ca,Mn)); U.S. Pat. No. 4,122,107 (Sb/Zn(Ca,Mn)); U.S. Pat. No. 4,356,299, U.S. Pat. No. 4,501,878, and U.S. Pat. No. 5,286,836 (Ti/Sb); U.S. Pat. No. 4,361,694 (Ti/Si): U.S. Pat. No. 4,468,489 (Ti,Zr,Ge,Zn); U.S. Pat. No. 4,499,226 and U.S. Pat. No. 5,019,640 (Sb/Co); U.S. Pat. No. 5,008,230 (Co(Zn)/Zn(Mn,Mg,Ca)/Sb); U.S. Pat. No. 5,138,024 and U.S. Pat. No. 5,340,909 (Zn/Sb); U.S. Pat. No. 5,565,545 and U.S. Pat. No. 5,644,019 (Sb/Ge); U.S. Pat. No. 5,596,069 (Co/Al); U.S. Pat. No. 5,608,032 and U.S. Pat. No. 5,623,047 (Sb/Co(Mg,Zn,Mn,Pb)); U.S. Pat. No. 5,656,221 (Sb/Co/Mn); U.S. Pat. No. 5,714,570 (Sb/Ti/Zn); and U.S. Pat. No. 5,902,873 (Ti(Zr)/lanthanide). At least one constituent of these complex catalysts is a xe2x80x9cclassicalxe2x80x9d polycondensation catalyst, either antimony, titanium, or germanium.
Finely dispersed titanates are the subject of U.S. Pat. No. 5,656,716. Jointly precipitated titanium and silicon compounds and titanium and zirconium compounds are described in U.S. Pat. Nos. 5,684,116 and 5,789,528.
A polycondensation catalyst on the basis of zeolites (alkali or alkaline earth metal-modified aluminosilicate) is protected in U.S. Pat. No. 5,733,969. The use of titanium compounds leads to yellowing of the polyester produced during polycondensation and processing. Especially during the use of polyethylene terephthalate as a food packaging, this color is undesirable.
The use of antimony as a catalyst is permitted only within precisely established boundaries, since this substance, as a heavy metal, is physiologically problematic.
The goal of this invention is to discover a catalyst system for the polycondensation, especially of polyethylene terephthalate, polybutylene terephthalate, or polytrimethylene terephthalate, which is physiologically safe and makes it possible to use the polycondensation products for food packaging. In terms of catalytic activity in polycondensation and selectivity, it must be compatible with conventional catalysts and must not influence the processing properties of polyester at all or only to the desired degree.
Quite surprisingly, it was found that complex compounds with hydrotalcite-analogous structures of the general formula [M(II)1xe2x88x92xM(III)x(OH)2]x+(Anxe2x88x92x/n).mH2O, (the use of which was previously described only as a filler (U.S. Pat. No. 5,362,457; U.S. Pat. No. 5,225,115; JP 09 077,962; JP 02 308,848; JP 61 118,457; JP 56 059,864), in olefin isomerizations, as an adsorbents (halogen trapper), as a carrier material for catalysts, flame retardant, molecular sieve, anion exchanger and catalyst for alcohol reactions (isophorone synthesis), hydrogenations, polymerizations, and reforming reactions (F. Cavani, F. Trifiro, A. Vaccari, Catalysis Today 11 (1991), 173-301)), before or after calcination, alone or in combination with phosphorus compounds that contain at least one hydrolyzable phosphorus-oxygen compound, are excellently suited for catalysis of polycondensation reactions, especially for the production of polyalkylene terephthalate.
In the formula mentioned, M(II) represents divalent metals, preferably Mg or Zn or Ni or Cu or Fe(II) or Co, and M(III) represents trivalent metals, preferably Al and Fe, and A represents anions, preferably carbonates or borates or titanyl compounds.
The particle size of the hydrotalcite used falls in the range of 0.1 to 50 xcexcm, preferably 0.5 to 5 xcexcm.
The calcination of the hydrotalcites can be performed at temperatures of 200xc2x0 C. to 800xc2x0 C., preferably at 400xc2x0 C. to 650xc2x0 C.
As phosphorus compounds which contain at least one hydrolyzable phosphorus-oxygen bond, phosphoric acid esters or esters of phosphorous acid can be used.
The catalyst system in accordance with the invention is used in the concentration ratio of hydrotalcite to phosphorus compound of 1:0.5 to 1:4, preferably 1:1 to 1:2.
The untreated or the calcinated hydrotalcite-analogous derivatives in combination with phosphorus compounds as stabilizers with at least one hydrolyzable phosphorus-oxygen bond show increased catalytic activity and selectivity in comparison to conventional catalysts and are characterized by high food compatibility.
It has been found that these substances, made up of several components, are highly catalytically selective, relatively independent of their composition, although the individual constituents catalyze polycondensation reactions either not at all or only with a very low selectivity and thus generate a high fraction of byproducts. It was also found that with the targeted selection of the constituents, surprisingly it was possible to influence the applications properties of the polyesters, for example the crystallization behavior. The polycondensation with the catalyst system in accordance with the invention is carried out under vacuum in a liquid phase at temperatures of 230xc2x0 C. to 280xc2x0 C. or in a solid phase at temperatures of 170 to 240xc2x0 C.
The addition of phosphorus compounds with at least one hydrolyzable phosphorus-oxygen bond leads to improved thermal stability of the polyesters, especially in the industrially required long residence times of the liquid polyesters under normal pressure in comparison to polyesters produced with conventional [catalysts], for example with catalysts on the basis of antimony and titanium compounds, but also in comparison to products produced under hydrotalcite catalysis.
Through the combination of hydrotalcite-analogous compound/stabilizer, molecular weight degradation and discoloration of the polyester can be lowered significantly without a negative influence on other important processing properties of the polyester, for example the crystallization behavior and the clarity of the final product.
In the following, the invention will be explained on the basis of exemplified embodiments.
In a 250-ml, single-necked flask with agitator and distillation attachment, 100 g precondensate of terephthalic acid and ethylene glycol with an average molecular weight was placed together with the catalyst. This apparatus was evacuated to about 0.5 mbar and purged with nitrogen. This process was repeated a total of three times. The glass flask was dipped into a hot salt bath at 280xc2x0 C. and the precondensate allowed to melt at this temperature. As soon as the melting was complete, vacuum was carefully applied.
Following termination of the polycondensation by purging with nitrogen, the product was allowed to cool in the flask, and the polyester was characterized according to its separation from the adhering glass.
The intrinsic viscosity (IV) was determined on an apparatus from the Schott Company (AVSPro) of 250 mg resin dissolved in 50 ml phenol/dichlorobenzene (1:1).
DSC measurements were performed on a Perkin-Elmer DSC 7.
The acetaldehyde determination took place according to the following procedure:
The PET material was precooled in liquid nitrogen and ground in an ultracentrifuge mill. The ground material was immediately weighed into a headspace vial and closed gas-tight with a septum. After holding a constant quantity of gas at 150xc2x0 C. for 90 minutes in the headspace sampler, the gas was injected onto the GC column, at a defined pressure. The color numbers were determined with a LUCI 100 spectrophotometer from the Lange Company.
Table 1 contains characteristic values of polyesters that were obtained by polycondensation reactions at temperatures of 280xc2x0 C. using various hydrotalcite catalysts.
Table 1 clearly shows that all tested untreated or calcinated hydrotalcite-analogous derivatives have catalytic activity. The synthesized polyethylene terephthalate, depending on the catalyst used, has different processing-related properties.
An additional important criterion for assessing the suitability of untreated or calcinated hydrotalcite-analogous derivatives is their catalytic activity in so-called solid state polymerization (SSP).
For these experiments, six of the polyesters listed in Table 1 were subjected to SSP. For this purpose the products were left for 96 hours at 200xc2x0 C. in a vacuum drying oven. After cooling, characteristic values relevant for applications technology were determined.
The results of solid state polymerizations of polyethylene terephthalate are summarized in Table 2.
Table 2 shows the fundamental suitability of the untreated or calcinated hydrotalcite-analogous derivatives as catalysts for polycondensation reactions in both liquid and solid phase.
It is especially important that it is possible by selecting the constituents of these complex catalysts to systematically influence the process technology properties of the polyester resins, for example the crystallization behavior.
The use of the hydrotalcite catalysts in accordance with the invention in combination with phosphorous compounds which contain at least one hydrolyzable phosphorus-oxygen bond is described in the examples that follow.